Multi-band mixed-signal hysteresis current control for EMI reduction in switch-mode power supplies

Switched mode power supply (SMPS) is used in majority of portable devices and plays the central role for energy-efficient power management. Recent developments in digital VLSI allow high performance control implementation with ultrafast recovery and high power density. However, electromagnetic interference (EMI) is a major concern in SMPS, which interferes with nearby devices and input power lines. This paper proposes a multi-band mixed-signal hysteresis current control (MBMSHCC) technique in a DC-DC converter. This considers the fast-changing current-loop in the analog domain, whereas a digital voltage controller Gc(z) is used to achieve fast recovery through real-time configuration. This achieves robust stability and parameter insensitive current ripple by sampling the output voltage at the rising edge of the high side gate signal. Closed-loop stability is shown to be insensitive to the input voltage, but it is dependent on the capacitor ESR. Thus a stable behaviour is achieved over a wide input voltage range, even under periodic modulation of the hysteresis band. This periodic multi-band operation significantly reduces the spectral peaks with insignificant impact on the ripple parameters and the transient performance. A synchronous buck converter prototype is made, and the proposed scheme is implemented using an FPGA device.